I can't find any rules in the rule book about this.What are you suppose to do when you can not follow the instruction on a card?Two questions:

1.If there are no cards left in the deck and you have Old Map as one of your cards, can you still play it?My guess would be yes because you could be sitting with two old maps on the last turn.

2. If you are allowed to play a old map as your last card you can obviously not look at the top card but are you still allowed to shuffle the ruins? The wording on the cards uses "then" so that would imply that you would not be allowed.

My group is still arguing about the keyword "then". Is there a official ruling or FAQ that could help me settle this?

Well, if there's no card in the deck to place in the ruins, then there's no reason to shuffle the ruins, the way I read it is, you look at the top card of the deck and place it in the ruins. Then you may shuffle the ruins, well, i read that as you have to put a card from the top of the deck into the ruins, then you may shuffle the ruins. Not sure if that's official, but that's how I play, because it makes the most sense, cause other than that, what would be the point of suffling, as if there are no other cards in the deck, then you wouldn't know what it is, hence, no need to shuffle